Apparatus for monitoring and controlling spontaneous firing of stored coal

ABSTRACT

Thermocouples are suspended to extend vertically and centrally of a coal reservoir to sense temperatures of coal at vertically plural points. When at least one of temperatures of coal sensed exceeds a preset temperature, a purge command signal is output by a controller to an inert gas valve. When a temperature increase rate of at least one of the coal temperatures sensed exceeds a preset rate, a water spraying command signal is output by the controller to a water spraying valve.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for monitoring andcontrolling spontaneous firing of stored coal.

2. Description of the Related Art

Generally, coal used as fuel for a gasifier, a boiler or the like isstored in a coal reservoir such as a bunker or a silo. In particular,lignite coal and subbituminous coal tend to spontaneously fire due tohigh volatile thereof and require sufficient attention.

Conventionally, monitoring of spontaneous firing of coal stored in acoal reservoir is usually performed by temperature measurement in thereservoir.

State-of-the-art technology for an apparatus of monitoring spontaneousfiring by temperature measurement of coal stored in a coal reservoir isdisclosed, e.g., in JP 11-230835A.

SUMMARY OF THE INVENTION

However, for a coal reservoir with a greater cross-sectional area, mostof conventional monitoring apparatuses can conduct temperaturemeasurement of coal only adjacent to a wall of a reservoir, which cannotbe necessarily regarded sufficient to monitor spontaneous firing ofcoal. Even in an apparatus disclosed in JP 11-230835A, temperaturemeasurement can be made only for coal adjacent to a bottom center of acoal reservoir, which cannot be necessarily regarded sufficient tomonitor spontaneous firing of coal.

Tests actually conducted by the inventor to verify spontaneous firingphenomenon of coal revealed that firing is triggered by temperatureincrease of stored coal centrally of a coal reservoir. It is, therefore,highly desirable to monitor a temperature of stored coal centrally of acoal reservoir.

The invention was made in view of the above and has its object toprovide an apparatus for monitoring and controlling spontaneous firingof stored coal capable of reliably sensing temperatures of stored coalcentrally of a coal reservoir and preventing spontaneous firing of coalfrom occurring.

The invention is directed to an apparatus for monitoring and controllingspontaneous firing of stored coal comprising

temperature detection means suspended to vertically extend centrally ofa coal reservoir for sensing temperatures of coal at vertically pluralpoints,

inert gas purge means for supplying inert gas into said coal reservoirand

a controller for outputting a purge command signal to said inert gaspurge means when at least one of the coal temperatures sensed at thevertically plural points by said temperature detection means exceeds apreset temperature.

According to the above apparatus, the following effects and advantageswill be obtained.

With the apparatus constructed as mentioned in the above, thetemperature detection means suspended to vertically extend centrally ofthe coal reservoir senses the coal temperatures at the vertically pluralpoints, so that temperature change of the stored coal centrally of thecoal reservoir can be grasped. When at least one of the coaltemperatures sensed by the temperature detection means at the verticallyplural points exceeds the preset temperature, a purge command signal isoutput by the controller to the inert gas purge means, so that inert gasis supplied from said inert gas purge means into the coal reservoir toprevent temperature increase of coal involved in oxidation thereof.

The apparatus for monitoring and controlling spontaneous firing ofstored coal may further comprise means for spraying water in said coalreservoir,

a water spraying command signal being output by said controller to saidwater spraying means when a temperature increase rate of at least one ofthe coal temperatures sensed by said temperature detection means exceedsa preset rate. Thus, the fact that the temperature increase rate of atleast one of the coal temperatures sensed by the temperature detectionmeans at the vertically plural points exceeds the preset rate isregarded as occurrence of spontaneous firing and water is sprayed by thewater spraying means in the coal reservoir, enabling reliableextinction.

In the apparatus for monitoring and controlling spontaneous firing ofstored coal, said temperature detection means may comprise a pluralityof thermocouples extending through a flexible metal tube, an outerperiphery of said flexible metal tube being covered with wire ropes.This makes it possible to exert high durability and high impactresistance under a severe service condition in the coal reservoir to andfrom which coal is supplied and discharged.

In the apparatus for monitoring and controlling spontaneous firing ofstored coal, temperature change of the stored coal centrally of the coalreservoir can be reliably sensed to prevent spontaneous firing of coalfrom occurring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic overview showing an embodiment of an apparatus formonitoring and controlling spontaneous firing of coal according to theinvention;

FIG. 2 is a sectional view showing thermocouples used as temperaturedetection means in the apparatus for monitoring and controllingspontaneous firing of coal according to the invention;

FIG. 3 is a sectional view showing a testing device verifyingspontaneous firing phenomenon of coal; and

FIG. 4 is a diagram showing temperature change of coal obtained in atest using testing devices of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the invention will be described in conjunction with theattached drawings.

FIGS. 1 and 2 show the embodiment of an apparatus for monitoring andcontrolling spontaneous firing of stored coal according to the inventionin which reference numeral 1 denotes a coal reservoir such as a bunkeror a silo for storage of coal used as fuel in a gasifier, a boiler orthe like. Suspended centrally of the coal reservoir 1 to verticallyextend is temperature detection means 2 which senses coal temperatures 2d at vertically plural points (three in the figure).

In the embodiment, the temperature detection means 2 comprises, as shownin FIG. 2, three thermocouples 2 a coated with FEP (Fluorinated EthylenePropylene) and extending through a flexible metal tube 2 b made ofstainless steel, an outer periphery of the flexible metal tube 2 b beingcovered with wire ropes 2 c, so that high durability and high impactresistance can be exerted under a severe service condition in the coalreservoir 1 to and from which coal is supplied and discharged. Thethermocouples 2 a illustrated are three in number to sense the coaltemperatures 2 d at vertically three points centrally of the coalreservoir 1; needless to say, the thermocouples may be two or more thanthree to sense the coal temperatures 2 d at vertically plural pointscentrally of the coal reservoir 1.

The coal reservoir 1 is provided with inert gas purge means 3 to supplynitrogen or other inert gas 1 into the coal reservoir 1 as well as means4 to spray water in the coal reservoir 1.

The inert gas purge means 3 comprises an inert gas cylinder 3 a chargedunder pressure with nitrogen or other inert gas, an inert gas supplypiping 3 b extending from the cylinder 3 a and connected to the coalreservoir 1 and an inert gas valve 3 c incorporated in the inert gassupply piping 3 b.

The water spraying means 4 comprises a water reservoir 4 a for storageof water for water spraying, a water supply piping 4 b extending fromthe water reservoir 4 a to an upper position in the coal reservoir 1, awater squeeze pump 4 c incorporated in the water supply piping 4 b, awater spraying valve 4 d incorporated in the water supply piping 4 b andon a discharge side of the water squeeze pump 4 c and water sprayingnozzles 4 e attached to the water supply piping 4 b at the upperposition in the coal reservoir 1.

Further arranged is a controller 5 to which input are the coaltemperatures 2 d at the vertically plural points sensed by thethermocouples 2 a of the temperature detection means 2. When at leastone of the coal temperatures 2 d sensed at the vertically plural pointsby the thermocouples 2 a of the temperature detection means 2 exceeds apreset temperature (e.g., 80° C.), a purge command signal 3 d is outputby the controller 5 to the inert gas valve 3 c of the inert gas purgemeans 3. When a temperature increase rate of at least one of the coaltemperatures 2 d sensed by the thermocouples 2 a of the temperaturedetection means 2 exceeds a preset rate (e.g., 1° C./min), a waterspraying command signal 4 f is output by the controller 5 to the waterspraying valve 4 d of the water spraying means 4.

FIG. 3 shows a testing device used in a test actually conducted by theinventor to verify spontaneous firing phenomenon of coal; with respectto a layer of pulverized coal charged in test cells 6 as receptacles forfiring temperature test, temperature change with time is measured tomonitor behaviors of temperature increase of coal leading to spontaneousfiring of coal.

In the test, pulverized coal classified into particle size of less than200 meshes (74 μm) and dried is charged into three kinds of test cells 6different in height and in inner diameter so as to have different layerheights H and diameters D of pulverized coal as shown in Table 1, thetest cells 6 being arranged in a thermobath (not shown) kept to apredetermined atmosphere temperature (e.g., 141° C.). With thethermocouples 2 a being set centrally of the test cell 6 at height halfas high as the layer height H and being set about 10 mm apart from aninner wall surface of the test cell 6 (about 5 mm apart from the wallsurface in a case of layer height H and diameter D being respectively 30mm) at height half as high as the layer height H, respectively,temperature change with time of the pulverized coal layer and presenceor absence of spontaneous firing are measured. In order to allow oxygensupply not only on an upper surface of but also on a side surface ofaccumulated pulverized coal just like real apparatuses, a side wall 6 aof each of the test cells 6 was made of alumina paper with thickness of3 mm. A bottom plate 6 b of each of the test cells 6 was made ofstainless steel with thickness of 1 mm.

TABLE 1 layer height diameter coal sample H mm D mm amount g 30 30 about10  60 60 about 100 100 100 about 450

It was ascertained in any of the three kinds of test cells 6 thattemperature change with time of layer center and layer periphery havetendencies as shown in FIG. 4. Specifically, it was ascertained that,though temperature of layer periphery is generally higher thantemperature of layer center because of temperature transferred to thepulverized coal charged in the test cell 6 through the opened uppersurface and the periphery of the test cell, the temperature of layerperiphery is moderate in change and abrupt change thereof leading tofiring is difficult to sense and that eventually the layer center hasabrupt temperature change (about 1° C./min or so) sooner than the layerperiphery, leading to firing at the layer center. From such reason, itis highly desirable to monitor the coal temperatures 2 d centrally ofthe coal reservoir 1.

Next, an operation of the above embodiment will be described.

With the apparatus constructed as mentioned in the above, the coaltemperatures 2 d at the vertically plural points are sensed by thethermocouples 2 a of the temperature detection means 2 suspendedcentrally of the coal reservoir 1 to extend vertically, so thattemperature change of the stored coal centrally of the coal reservoir 1can be determined. When at least one of the coal temperatures 2 d at thevertically plural points sensed by the thermocouples 2 a of thetemperature detection means 2 exceeds a preset temperature (e.g., 80°C.), the controller 5 outputs a purge command signal 3 d to the inertgas valve 3 c of the inert gas purge means 3, so that inert gas valve 3c is opened to supply inert gas from the inert gas cylinder 3 a into thecoal reservoir 1 through the inert gas supply piping 3 b to therebyprevent temperature increase upon oxidation of the coal.

When a temperature increase rate of at least one of the coaltemperatures 2 d at the vertically plural points sensed by thethermocouples 2 a of the temperature detection means 2 exceeds a presetrate (e.g., 1° C./min), it is regarded as occurrence of spontaneousfiring and water spraying command signal 4 f is output by the controller5 to the water spraying valve 4 d of the water spraying means 4, so thatthe water spraying valve 4 d is opened and water is supplied from thewater reservoir 4 a via the water supply piping 4 b into the coalreservoir 1 by driving the water squeeze pump 4 c and is sprayed by thewater spraying nozzles 4 e. Thus, extinction can be conducted reliably.

Moreover, the fact that the temperature detection means 2 comprises, asshown in FIG. 2, the three thermocouples 2 a coated with FEP extendingthrough the flexible metal tube 2 b made of stainless steel or the like,the outer periphery of the flexible metal tube 2 b being covered withthe wire ropes 2 c, makes it possible to exert high durability andimpact resistance under a severe service condition in the coal reservoir1 to and from which coal is supplied and discharged.

Thus, temperature change of stored coal centrally of the coal reservoir1 can be reliably sensed and spontaneous firing of coal can be preventedfrom occurring.

It is to be understood that an apparatus for monitoring and controllingspontaneous firing of stored coal according to the invention is notlimited to the above embodiment and that various changes andmodifications may be made within a gist of the invention.

1. An apparatus for monitoring and controlling spontaneous firing of stored coal comprising temperature detection means suspended to vertically extend centrally of a coal reservoir for sensing temperatures of coal at vertically plural points, inert gas purge means for supplying inert gas into said coal reservoir and a controller for outputting a purge command signal to said inert gas purge means when at least one of the coal temperatures sensed at the vertically plural points by said temperature detection means exceeds a preset temperature.
 2. The apparatus for monitoring and controlling spontaneous firing of stored coal as claimed in claim 1, further comprising means for spraying water in said coal reservoir, a water spraying command signal being output by said controller to said water spraying means when a temperature increase rate of at least one of the coal temperatures sensed by said temperature detection means exceeds a preset rate.
 3. The apparatus for monitoring and controlling spontaneous firing of stored coal as claimed in claim 1, wherein said temperature detection means comprises a plurality of thermocouples extending through a flexible metal tube, an outer periphery of said flexible metal tube being covered with wire ropes.
 4. The apparatus for monitoring and controlling spontaneous firing of stored coal as claimed in claim 2, wherein said temperature detection means comprises a plurality of thermocouples extending through a flexible metal tube, an outer periphery of said flexible metal tube being covered with wire ropes. 